A rotary ball valve is a valve having a spherical ball that controls the flow of a fluid through it. The spherical ball has a through path or bore, which, when is co-axial with the inlet and outlet port of the valve leads to opening of the valve, allowing the flow of the fluid to occur. In the closed position, the through path or bore is substantially at right angle with the inlet and outlet port of the valves. The ball valve, for the purpose of describing present invention, could be either a trunnion ball valve or a floating ball valve, or an improvisation of either.
The direction from which flowing fluid approaches the ball is generally known as an upstream while the direction away from the ball, along which a flowing fluid leaves the valve, is known as a downstream.
In a trunnion ball valve, the ball is anchored on bearing or on pivot whereas its seals float. The seals in the trunnion valve are externally energized using springs. As the seal floats under fluidic pressure the upstream seal presses against the ball and it is therefore active, while the downstream seal is inactive. In a floating ball valve, wherein the ball floats and the seal is firmly held in the body, the seals are self-energizing. As the ball floats under fluidic pressure the downstream seal is active while the upstream seal is inactive.
In both the cases, whether trunnion ball valve or floating ball valve, one of the main requirements is that the rotary ball valve does not leak, and particularly, no fluid reaches the downstream side when the valve is closed. Leakage is most probable between joints and between relatively moving components.
The leakage is prevented by providing sealing between the two joining parts or two relatively moving parts. The seal is generally of an elastomeric material, which is relatively softer than metallic materials, of which are made the ball, valve body, operating shaft and other parts of the rotary valve.
Patent Publication No: CN 201069001Y claims to disclose a fixed ball (trunnion) type zero-leakage ultra-high-pressure ball valve wherein seal of different locations within a valve are generally described, for example, use of elastomeric seal at fixed and moving joints, O-ring at the rotating shaft, et cetera, though the novel and inventive aspect of the disclosure is not quite clear.
U.S. Pat. No. 3,554,485 is one such earlier invention disclosing a seal in the form of a seat ring to seal against the surface of the ball along with a seat-retaining ring, supporting said seat ring. The disclosure mentions a seat ring and a wedge ring, both preferably of Polytetrafluorethylene, commonly known as PTFE.
Use of O-ring in general and for sealing in rotary ball valves is known. This is illustrated in U.S. Pat. Nos. 3,445,087, 2,480,529, 4,111,393, 4,781,213, 4,911,408, 6,948,699B1, Patent Application No: US201201120110 and Patent Application No: EP2341269A1 that deploys O-ring for sealing stationary joint or moving component, whether stand alone or in combination with seat ring. U.S. Pat. No. 4,335,748 which describes a disc valve, also uses O-ring, and this patent is cited here merely to amply illustrate the generic application of O-ring.
There are valve designs for use in extreme conditions. Example: Valves that can be used to carry fluids at high temperature, of the order of 500° C., and or valves that carry inflammable fluids wherein sealing is also expected to prevent spread of fire once the valve is closed. U.S. Pat. No. 4,286,614 and U.S. Pat. No. 6,669,171B1 describe such ball valves which are capable of sealing effectively against fluid leakage in the presence of fire conditions by providing a metal to metal sealing after the elastomeric seal has burnt away due to fire. U.S. Pat. No. 4,911,408 in addition, facilitates top assembly of the ball. U.S. Pat. No. 8,328,160 divulges valve for another extreme condition when cryogenic fluids are handled and the ball valve needs to provide sealing at temperatures of about minus 250° C.
As indicated above, in a floating ball valve or in a trunnion ball valve, the effective sealing takes place only either at upstream side or a downstream side. In other words the blocking action is achieved at one side only. If the seal of that side leaks, then the rotary ball valve loses the very purpose of its deployment. To counter this situation, there are disclosures to invent combination valves which are a modification of a floating ball valve and a trunnion ball valve. Patent application No: EP1680614A1, also published as WO2006024860A1 describes a double block valve wherein seals of both sides, that is, the upstream side as well as the downstream side contribute in sealing the flow of fluid. The disclosure also includes relief valves. While the aim of the disclosure appears to prevent leakage, the disclosure does not include nor address a seal design as such. U.S. Pat. No. 8,398,053B2 also discloses an arrangement for both side sealing with respect to the ball. Such designs are known as double block type and are generally provided with a bleed valve, referred to as relief valve above.
Whether single or double sealing, the construction and fitment of the seal is important factor. The seal itself should not distort under pressure. U.S. Pat. No. 3,604,682 discloses a wedge assembly comprising of a sealing ring and backing ring to prevent displacement of the sealing ring. The wedge seal assembly has conical mating faces of the sealing ring and the backing ring, and includes a complementary inter-fitting ridge and recess thereon.
Dislodging or loosening of the seal under pressure is a known field problem. U.S. Pat. No. 4,135,545 provides a non-metallic seal for a valve seat assembly which has a substantial resistance to being blown out during high velocity low rate conditions by swaging of the metallic seat member to lock the non-metallic seat member in place.
U.S. Pat. No. 3,729,015 discloses a rotating seat so as to distribute the wear pattern thereby enhancing the life and effectivity of the seal.
U.S. Pat. No. 4,111,393 discloses a removable seal in order to facilitate repair of the valve.
One of the practical situations, which is unaddressed by prior art, is effectivity of seal under wide variation of temperature. The seal loosens in its seat, due to thermal cycling. The situation worsens in case of double block and bleed condition. While a sealing may be effective at a particular temperature and pressure, it may not be suitable when the pressure and temperature vary, even if below or within the highest value for which a sealing of a valve is designed.
Thus there is a need in the art to develop effective sealing between a ball and the seat for a ball valve assembly for preventing fluid leakage under ambient temperature variation and under temperature variation at higher pressure as well as at low pressure. The present invention addresses the above mentioned need effectively.